This Application is the U.S. National Phase Application of PCT International Application No PCT/GB00/03344 filed Sep. 1, 2000. This invention relates to apparatus for use in handling a load which is capable of raising and lowering, or of towing, a load and also handling service cables and/or hoses connected to the load. The invention is particularly, but not exclusively, applicable to the handling of subsea equipment such as grabs.
Hitherto, providing services to underwater equipment has required the provision of a specific bundle of cable(s) and/or hose(s) dedicated to each application. For some applications, it is known to incorporate the service bundle within an armoured hoist rope. This approach has a number of deficiencies. The resulting rope is costly, gives inferior hoisting properties, and by virtue of limitations on the diameter of rope which can be handled the services which can be incorporated are limited. Further, in practice it is impossible with this arrangement to add to the length of the rope or to join different types of materials, for example wire ropes with fibre ropes.
In accordance with an aspect of the present invention, apparatus for use in handling a load comprises a load-bearing rope, a mechanism for paying out and recovering the rope, a mechanism for holding a and paying out a service cable, and a wrapping device for rotating said rope around the service cable as the cable is payed out to wrap the rope around the service cable, and to unwrap one from the other as either of them is recovered.
In accordance with another aspect of the present invention, a method of handling a load comprises paying out a service cable and wrapping a load-bearing rope around the service cable as it is payed out, and subsequently unwrapping one from the other as either of them is recovered.
Winding the load-bearing rope around the cable as it is paid off from a static cable winch allows use of large diameter cables. When the wound cable and rope leave the device, the higher tension on the rope pulls that into an axial configuration with the service cable helically coiled around it, ensuring that the load is then borne by the rope and not the cable.
The term xe2x80x9cservice cablexe2x80x9d is used herein to denote a flexible elongate member used for conveying power or data, such as an electrical cable, a fibre optic cable, or a pneumatic or hydraulic hose.
Preferably, the rope is wrapped helically around the service cable as it is being paid out. The rope and the service cable are preferably both tensioned when being paid out, and the tension typically applied to the load-bearing rope is typically higher than the tension applied to the service cable.
As the rope and service cable leave the apparatus the higher load on the rope wrapped around the service cable straightens the service cable and wraps the service cable helically around the rope. This allows larger diameter service cables to be used with any type of load-bearing rope without modifications to the winding apparatus used for winding the rope around the axial service cable. Therefore, the service cable can be paid out from a large drum on a static main winch of the device rather than needing to be mounted on a drum of fixed size which is arranged to rotate around an axis, thereby reducing the limitations on the diameter and length of the service cable to be paid out. Also, the service cable on the main winch can be connected to the services as it is being paid out, thereby allowing services to be provided as the load is lowered or raised, e.g. electricity can be supplied to an ROV without disconnection of supply in order to change reels of service cable. In contrast the rope can be dispensed from the service cable and joined to additional lengths of rope as required, again without disrupting the provision of services to the load.
The drum for paying out the rope is typically arranged such that the rope leaves the drum at or close to the axis of the cable so that the rope does not exert sideways force on the cable. Rollers or other such devices can be used to deflect the cable momentarily from the axis to allow the rope to be paid out along or close to the axis.
Typically, the load-bearing rope will be a hoist rope used for raising and lowering a load. Alternatively, the load-bearing rope may be a towing rope used for paying out, towing and recovering a load such as a marine sensor array.
The apparatus may include a plurality of service cables each extending from a respective drum.
The rope is preferably paid out from a drum arranged to rotate around the axis of the service cable.
Preferably, the mechanism for paying out and recovering the service cable comprises a cable winch, from which the cable passes over a cable sheave and thereafter may extend to the load along a substantially straight axis.
The wrapping device may comprise the rope drum being arranged for rotation about a drum axis which coincides with the axis of the service cable, the drum typically having a central aperture through which the service cable passes, the rope preferably passing over a rope sheave which is mounted for movement in a circular path around said axis.
Alternatively, the rope drum may be rotatable on a structural member that is arranged for movement in a circular path about said axis.
Alternatively the rope drum may be static and a winding device can rotate around it to pay out the rope.
The service cable winch, the rope drum, and the wrapping device may conveniently each have a respective driving motor; they could however be driven by a single source through appropriate mechanical linkages.
Certain embodiments are likely to be useful when a large diameter or heavy signal/power is used and it is more convenient to store the cable on a large winch cable bin, or flaked out in lengths and subsequently joined. Smaller load bearing ropes can be stored on the mechanism, and can also be used for hoses and telecommunications cables.
The hoist rope winch is rotated around the central signal/power cable in order to twist the cable and the rope together as they are paid out and rotated in the opposite direction to untwist them as the load is hoisted. Because the weight is on the hoist rope the result will have the appearance of the signal/power cable being wound around the hoist rope.
The hoist rope winch drum may be placed near the centre in order that the rope is paid out close to the centre line and double tapered rollers may be used to deflect the signal/power cable to one side in order to assist in maintaining the hoist rope near the centre.
In other embodiments the hoist rope winch is turned in combination with a rotating arm which may support spooling gear. This arm rotates around the central signal/power cable in order to twist the two cables together as they are paid out and rotated in the opposite direction to untwist the cables as they are hoisted.
The rotating arm may have guide sheaves to position the hoist rope near the centre and attached to these may be double tapered rollers to deflect the signal/power cable to one side in order to assist in maintaining the hoist rope in the centre.
One or more additional ropes can be provided, each with a respective rope drum and sheave arranged to rotate around the axis of the service cable if desired. Alternatively, other service cables can be wound around the main service cable in a similar manner to the hoist rope sheave.